1. Field of the Invention
The present invention relates to a sheet supplying device for supplying cut sheets, which are cut to predetermined sizes, to printers, facsimile machines or copy machines one sheet at a time. Specifically, the present invention relates to a cassette-type sheet supplying device where a plurality of cassettes, each holding cut sheets of sized paper, such as B5, A4, B4 and A3, can be installed to supply the desired sized sheets during printing or copying.
2. Description of Related Art
One known type of a cassette sheet supplying device is capable of having two or more cassettes installed at the same time, the device feeding a cut sheet from one of the cassettes by selectively driving a paper feeding unit associated with each cassette. According to this sheet supplying device, the size of the cut sheet can be selected. Usually, the size of the cassettes is such that the cassettes can be interchanged for one another. Thus, each such cassette can be installed in an arbitrary cassette mounting position. Therefore, each cassette accommodates essentially the same number of cut sheets.
However, some users occasionally want to use large quantities of a sheet of one size, such as B5 or A4 sheets. In order to respond to such demand, a type of sheet supplying device that can receive a large cassette capable of accommodating large quantities of cut sheets has been developed.
FIG. 11 schematically shows this type of sheet supplying device. Interchangeable standard cassettes can be installed in installation spaces 50, 52 and a large cassette can be installed in installation space 54.
This type of sheet supplying device is very convenient for a user who, for instance, always requires large quantities of sheets of A4 size and sometimes uses sheets of B5 or B4 size. However, it is not always convenient for the user who always uses sheets of various sizes and sometimes requires large quantities of a sheet of a specific size. For such users, the large cassette is unnecessary when variously sized sheets are required, and standard cassettes are unnecessary when large quantities of a specific size are required. For such a user, it is only necessary to be able to install plural standard cassettes or one large cassette. The device for such a user permits the installation space, or the sheet supplying device, to be miniaturized because it is unnecessary to install both the plural standard cassettes and the large cassette at the same time. With such a device as mentioned above, it is unnecessary to have a paper feeding unit for feeding the cut sheets from each of the plural standard cassettes and the large cassette and a paper feeding path for feeding the cut sheets from each cassette to the predetermined position. Therefore, the structure required for the large cassette only can be omitted.
FIGS. 10A and 10B show a conventional sheet supplying device having a plurality of standard cassettes and a single large cassette. A standard cassette S1 is installed in an installation space 50 and a standard cassette S2 is installed in an installation space 52. A large cassette L is installed in an installation space 54. A paper feeding unit 26(S1), for the cassette installed in the installation space 50, and paper feeding units 26(S2), 26(L), for the cassettes installed in the installation spaces 52, 54, respectively, are provided as shown.
In the conventional sheet supplying device thus constructed, it is impossible to install the large cassette in the spaces 50, 52. Moreover, even if the large cassette L could fit into the space, by combining openings 50, 52, it cannot be sealed properly because proper positioning is obstructed by the paper feeding unit 26(S2).